Technical Field
The present invention generally relates to carbon nanotube transistors, and more particularly to carbon nanotube field effect transistors employing intermetallic contacts and methods for fabrication.
Description of the Related Art
Circuits can employ carbon nanotubes (CNTs) for complementary metal oxide semiconductors (CMOS) having both electron carrier field effect transistors (nFETS) and hole carrier FETS (pFETs). For conventional semiconductor FETs, polarity of the carrier is determined by doping source/drain contacts, channel, and gate. CNT FETs function differently as the polarity of the carriers is determined by a work function of the source/drain contacts. For pFETs, a high work function metal, such as, Pd is commonly used. This works well, because high work function metals are chemically inert, so a stable contact can be obtained.
However, in making nFET devices, difficulties arise in using low work function metals. These materials react very strongly with oxygen, forming non-conducting oxides. This has two deleterious effects. By creating an insulating layer, a series resistance is added to the device, lowering the amount of current that can be transmitted. Also, by gettering oxygen from other insulators used in fabricating the device, leakage pathways are created, in particular, between a bottom gate and the source/drain contacts. The problem is especially acute when hafnium oxide is used as an insulator, which is reduced to a sub-oxide when contacted by, e.g., low work function metals.